In a radio base station used in a mobile communication system, an abnormality of the base station function, such as discontinuation of a transmission radio wave, may occur for some reason, for example, due to a malfunction of internal software or hardware. When an abnormality such as transmission radio wave discontinuation occurs in a radio base station, it is preferable that the abnormality be detected early in view of network operation. In the mobile communication system where the abnormality is detected, it is preferable that countermeasures against the detected abnormality be taken early to compensate for the detected abnormality. The countermeasures include a so-called compensational operation to operate radio base stations on the periphery of the radio base station where the abnormality is detected, a recovery from the abnormal state, and so forth.
An example of the compensational operation is described below. After the abnormality of the radio base station is detected, other radio base stations on the periphery of the radio base station where the abnormality occurs may communicate with a mobile terminal that has communicated with the radio base station where the abnormality occurs, so that a decreased operation of the mobile communication system is temporarily performed. Further, a method of making a recovery from an abnormality by using an element management system (EMS) managing a device or an element provided on a network may be considered. According to the method, upon being notified that an abnormality of a transmission radio wave or the like occurs in a radio base station managed by the EMS, the EMS resets the settings on radio wave transmission performed by the radio base station to recover from the abnormality.
On the other hand, notification of the abnormality is in some cases not appropriately performed depending on the type of abnormality occurring in a radio base station. For example, when a failure occurs in the abnormality detection function due to the occurrence of an abnormality relating to the radio base station, the abnormality detection is not performed. Further, when a failure occurs in the abnormality notification function, an appropriate notification is not made. Hereinafter, an abnormal state where a self diagnosis or an abnormality notification is not performed by a radio base station will be referred to as a non-alarm abnormal state.
The technology for detecting the non-alarm abnormal state has been studied as a functional element for the self organizing network (SON) use case in a so-called next generation radio communication network such as Third Generation Partnership Project—Long Term Evolution (3GPP-LTE) standard specifications, Next Generation Mobile Networks (NGMN), etc.
Japanese Unexamined Patent Application Publication No. 2006-340050, Japanese Unexamined Patent Application Publication No. 11-146443, and Japanese Unexamined Patent Application Publication No. 2005-340993 describe technologies relating to a method of detecting the occurrence of abnormality including the occurrence of non-alarm abnormal state; compensational operations when abnormality is detected; and processes to recover from an abnormality.